The Labour peer Lord Lipsey, who said he understood there was a range of views on the subject, complained that the ad was misleading for claiming experts were in agreement.

Greenpeace said the claim was made in the context of a public debate on Government policy, and cited quotes from David Cameron, who has repeatedly backed fracking and claimed that it could bring down energy bills.

The organisation provided quotes from 22 people, groups or organisations supporting the view that fracking would not reduce energy prices.

A demonstrator stands in the road as police escort a lorry to a site run by Cuadrilla Resources outside Balcombe (Reuters)

It said banning the ad would be a breach of Article 10 of the European Convention on Human Rights.

The Advertising Standards Authority (ASA) said consumers would interpret the claim that "experts agreed" to mean that there was a general consensus among those of informed opinion that fracking would not reduce energy bills.

It said: "While we acknowledged that Greenpeace had provided quotes from 22 people, groups or organisations demonstrating support for the view that fracking would not reduce energy prices, we understood that there was a significant division of informed opinion on the issue.

"This was demonstrated, for example, by the quotes provided by Greenpeace from the Prime Minister."

The ASA noted that only a minority of the quotes provided by Greenpeace decisively stated that fracking would not reduce the cost of energy bills, while others highlighted the unlikeliness of prices being cut or a lack of evidence.

It said: "While we understood the claim was made in the context of a public debate on fracking, we considered the claim was absolute in nature and therefore implied the statement was accepted among informed opinion, which we understood was not the case.

"Because of that, we concluded that the ad was misleading."

It ruled that the ad must not appear in its current form, adding: "We told Greenpeace to ensure they did not use claims that misleadingly implied their views were universally accepted if a significant division of informed opinion existed."